Shredding machines of the general type with which the present invention is concerned are well known, see for example Schwarz U.S. Pat. No. 3,880,361, which is incorporated herein by reference. Machines of this type are frequently used for shredding trash, sheet metal, automobile tires, etc. Typically, as shown in the Schwarz patent, a pair of parallel rotatable knife carrying shafts have sets of knives or cutters axially interleaved which are rotated in opposite directions to shred material which is gravitationally fed to the knives. Because the material being shredded may, in many instances, include pieces of metal or other objects which exert substantial resistance to the shredding action of the knives, many of such machines are provided with a torque responsive control which will reverse the direction of rotation of the drive motor when a torque overload is sensed at the comminuting shafts. This reversal of direction of rotation of the comminuting shafts will disengage the teeth from the offending object and reposition the object by virtue of the reversal of the direction of rotation. Controls of this type are disclosed in the aforementioned patent.
The problem encountered with such controls is that the torque responsive, drive reversing control requires a finit time period to accomplish the drive reversal. We have determined that, when the comminuting teeth encounter an extremely hard object, the time delay between the sensing of the torque overload and the reversal of direction of rotation of the comminuting shafts may be too long to prevent the knives or teeth on the comminuter from being broken off or damaged.
The present invention is especially directed to a solution to this latter problem. U.S. Pat. Nos. 1,409,238, 2,273,772, 2,597,635, 3,423,033, 3,478,972, 3,845,906 and 3,918,648, disclose various mechanisms which have attempted to solve similar problems but are not deemed suited to the purposes of the applicant here. In the present instance, the casing of a drive transmission component in the drive line is so mounted that a torque overload on the comminuting shafts reacts to bodily rotate this casing relative to the fixed frame of the machine. Cushioning devices are provided to resiliently resist this movement of the casing, thus cushioning the impact and absorbing the resistance applied to the knives for a period sufficient to enable the drive to be reversed before damage to the knives occurs.